On an early fall afternoon in Ganges Chasma (Valles Marineris), we managed to capture a cluster of 8 dust devils (http://static.uahirise.org/images/2015/details/cut/ESP_042201_1715.jpg), five of them in the enhanced color strip. They’re together on a dark sandy surface that tilts slightly to the north, towards the Sun. Both of these factors help warm the surface and generate convection in the air above. The surface is streaked with the faint tracks of earlier dust devils. A pair of dust devils appears together at top right, spaced only 250 meters apart. These two have quite different morphologies. The bigger one (on the right) is about 100 meters in diameter and is shaped like a doughnut with a hole in the middle. Its smaller companion is more compact and plume-like, but it too has a small hole in the center, where the air pressure is lowest. It may be that the smaller dust devil is younger than the larger one. A row of four dust devils are in the middle of the color strip, separated by about 900 meters from one another. This image might answer some interesting questions about the behavior of dust devils. Dust devils are theoretically expected to migrate uphill on a sloping surface, or migrate downwind when there is a breeze. Where they are found close together in pairs, they are expected to rotate in opposite directions. HiRISE color observations can be used to determine the direction of rotation and—for fast moving dust devils—the direction of their travel. This is because the different color observations (infrared, red, and blue) are taken at slightly different times. The differences between the earliest color observation and the last tell us about the changes that took place during that time interval. All this requires careful analysis, but if these dust devils are moving fast enough, and spaced closely enough, these here might display some interesting “social dynamics,” possibly marching together and rotating in alternating directions. Written by: Paul Geissler (4 November 2015) Related Media Dust Devil on Mars (Dust Storm): https://www.youtube.com/playlist?list=PL6vzpF_OEV8lrQ2tk89aC_FXVfhqftJSW Mars Seasonal Processes: https://www.youtube.com/playlist?list=PL6vzpF_OEV8n955tHhRwGP4o4IK5k8wrn HiRISE, High Resolution Imaging Science Experiment (Mars Reconnaissance Orbiter Instrument): http://www.youtube.com/playlist?list=PL6vzpF_OEV8nfAL7zVkUWJpw-_9jkJjtZ HiRISE, High Resolution Imaging Science Experiment: "Explore Mars, one giant image at a time." The Mars Reconnaissance Orbiter Project is managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., for NASA's Science Mission Directorate, Washington. JPL is a division of the California Institute of Technology in Pasadena. HiRISE is operated by the University of Arizona, Tucson. The instrument was built by Ball Aerospace & Technologies Corp., Boulder, Colo. Malin Space Science Systems, San Diego, built and operates the Context Camera. Credit: NASA/JPL/University of Arizona

• published: 05 Nov 2015
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